The present application concerns a master alloy for modification and grain refining of hypoeutectic and eutectic Alxe2x80x94Si based foundry alloys.
During todays production of aluminium-silicon foundry alloys, additives are used to modify and grain refine the casting structure. Small grains are desirable to among others obtain better castability and smaller pores, as well as better homogeneity and mechanical properties. A modified structure implies a finely divided silicon phase which gives a significant increase in ductility and strength.
Grain refining alloys usually contain aluminium, titanium and boron in a certain ratio. An increasingly more common Alxe2x80x94Tixe2x80x94B master alloy with a ratio 1:1 of Ti:B has been developed for foundry alloys and is described in the applicants"" own Norwegian patent application 19990813, not yet published.
Modification of the cast structure takes place by introduction of strontium/sodium/antimony to the melt, often by addition of an aluminium-strontium master alloy.
Common practice is to add modifying and grain refining elements and/or master alloys of these separately. With the present invention a novel alloy has been developed which combines Alxe2x80x94Tixe2x80x94B and strontium in one and the same product. The invention is characterized by that the content of Ti is between 0.5 and 2.0% by weight, the content of B is between 0.5 and 2.0% by weight and the content of Sr is between 3.0 and 12.0% by weight, and the ratio Ti/B is between 0.8 and 1.4.
With the alloy according to the present application a solution has been found to make it possible to simplify the addition practise in the foundries by achievement of modification and grain refining by addition of one and the same alloy. Trials show that modification and grain refining properties are at least equal to those achieved by separate addition of TiB alloy and Sr.